I was aware that non-EU nationals were banned from entering Greece after 6 am on 18 March but that report said that "Quarantine may be ordered for all others, especially British citizens." I wasn't aware of any ban or quarantine arrangement for EU, including UK, citizens as early as 16 March.
Article Monday 16th March ekathimerini
Press briefing on Monday 16th March...Deputy Civil Protection Minister Nikos Hardalias said that anyone arriving from abroad should place themselves into obligatory quarantine for two weeks, and refered specifically to those arriving from Britain, a country that has yet to apply strict measures to limit the spread of the virus.
The quarantine applies to anyone entering the country, regardless of nationality.
http://www.ekathimerini.com/250703/arti ... quarantine